1. Field of the Invention
The present invention relates to a combustor containing a fuel nozzle to supply fuel. Particularly, it relates to a gas turbine combustor.
2. Description of the Related Art
FIG. 1 shows an axial direction sectional view of a combustor containing a known fuel nozzle disclosed in Japanese Patent Application No. 2001-173005. As shown in FIG. 1, a pilot nozzle 300 is provided on an central axis of inner tube 180 of a combustor 100. A plurality of fuel nozzles 200, which extend substantially parallel to the pilot nozzle 300, are equally spaced in a peripheral direction around the pilot nozzle 300. Fuel is supplied to the pilot nozzle 300 and fuel nozzles 200. A swirl vane or a swirler 290 is disposed around a rodlike body of the fuel nozzle 200. A plurality of hollow columns 250 which radially and outwardly extend from the sidewall of the fuel nozzle 200 are provided on the fuel nozzle 200. The hollow columns 250 are connected to the fuel nozzle 200. A plurality of injection ports 260 are provided in each hollow column 250 to inject fuel toward a tip end of the fuel nozzle 200. A mixing chamber 150 is formed in the vicinity of the tip end of the fuel nozzle 200, and a pilot combustion chamber 160 is defined by a pre-mixing nozzle 170 in the vicinity of the tip end of the pilot nozzle 300.
The path of air for combustion that enters the combustor 100 through an air inlet 110 thereof is changed by about 180° at an inner tube end portion 120 to allow the air to flow into an air passage 140. A part of air for combustion is mixed with fuel injected from injection ports 260 of the hollow column 250 and, then, flows into the swirler 290 of the fuel nozzle 200. Accordingly, the air for combustion is rotated mainly in a peripheral direction and mixture of the air for combustion and the fuel is promoted. Thus, pre-mixed air is produced in the mixing chamber 150.
The remaining of air for combustion flows into the swirler 390 disposed between the pilot nozzle 300 and the pre-mixing nozzle 170. The air for combustion is burnt with fuel injected from the pilot nozzle 300, in the pilot combustion chamber 160, to produce a pilot flame. Pre-mixed air mixed with fuel injected from the injection ports 260 of the hollow column 250 is brought into contact with the pilot flame and then is burnt to produce a main flame.
FIG. 2a is a sectional view taken along the line A—A in FIG. 1. FIG. 2b is an enlarged sectional view of a fuel nozzle of a known combustor. As described above, a plurality of hollow columns 250 which radially and outwardly extend from the fuel nozzle 200 are provided on the fuel nozzle 200. As shown in FIG. 2b, a plurality of fuel injection ports 260 to inject fuel in a direction perpendicular to the airflow are formed in each hollow column 250. A plurality of injection ports 260 (for example, two injection ports 260 in FIG. 2b) are arranged, in a line, in the vicinity of a center of the width of the hollow column 250. There is a space between the injection port 260a that is most distant from an axis B of the fuel nozzle 200 and the inner wall 430 of the hollow column 250 that is most distant from the axis. In FIG. 2b, the length of the space is similar to a half of the distance between injection ports adjacent to each other. If the inner wall 430 of the hollow column 250 is adjacent to the injection port 260a, less fuel is injected from the injection port 260a than from other injection ports and, thus, such a space is necessary. As shown in FIGS. 2a and 2b, it is preferable that these plural hollow columns 250 be planar and, thereby, a flow with a low pressure drop and less volution can be produced. This is because the projected area of the hollow column 250 in the direction of the airflow can be minimized if the hollow column 250 is planar. Therefore, a pressure drop and volution of the flow can be reduced as the thickness of the planar hollow column 250 is reduced. The injection port 260 shown in FIG. 2b is a circle-shaped hole having a diameter of 1.8 mm, and a thickness 270 of a passage 410 of the hollow column 250 is 1.5 mm.
However, the thickness of the planar hollow column 250 is reduced, so that the thickness 270 of the passage 410 in the planar hollow column 250 is relatively reduced. Accordingly, the fuel passing through the hollow column 250 flows two-dimensionally. Thus, a vortex 900 occurs in the vicinity of a tip end 420 of the hollow column 250. If a plurality of fuel injection ports 260 are formed in one hollow column 250, the vortex occurs around the injection port 260a that is most distant from the axis B of the fuel nozzle 200. Therefore, it is difficult to inject fuel through the injection port 260a. Accordingly, the flow coefficient of the farmost injection port 260a is smaller than that of other injection ports, and a deviation of the flow coefficient between the farmost injection port 260a and the other injection ports is increased. Thus, the stability of injection of fuel is reduced as the flow coefficient is decreased. There is a possibility that a combustion vibration may occur because uniform pre-mixed air is not produced due to scattering of a flow coefficient.
If pre-mixed air in which a mixture of fuel and air is unbalanced is used, NOx is formed. Therefore, it is necessary to produce pre-mixed air having a uniform concentration to reduce NOx. However, in a combustor containing a fuel nozzle disclosed in Japanese Patent Application No. 2001-173005, the concentration of fuel becomes high in the vicinity of the axis B of the fuel nozzle 200 and becomes low in the vicinity of the injection port 260a due to the vortex 900. Accordingly, it is difficult to produce pre-mixed air that is uniformly mixed. It is preferable that the amount of fuel injected from the injection port be determined in accordance with only the size of the injection port, regardless of the distance of the injection port from the axis. In terms of reduction of NOx, it is necessary to avoid scattering of a flow coefficient in each injection port.
Therefore, the object of the present invention is to provide a combustor containing a fuel nozzle in which a vortex cannot occur in a hollow column.